Abstract

We present here a series of perylene diimide (PDI) based isomeric conjugated polymers for the application as efficient electron acceptors in all-polymer solar cells (all-PSCs). By copolymerizing PDI monomers with 1,4-diethynylbenzene (para-linkage) and 1,3- diethynylbenzene (meta-linkage), isomeric PDI based conjugated polymers with parallel and non-parallel PDI units inside backbones were obtained. It was found that para-linked conjugated polymer (PA) showed better solubility, stronger π-π stacking, more favorable blend morphology, and better photovoltaic performance than those of meta-linked conjugated polymers (PM) did. Device based on PTB7-Th:PA (PTB7-Th:poly{4,8-bis[5-(2-ethylhexyl)-thiophen-2-yl]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl)- carbonyl]thieno[3,4-b]thiophene-4,6-diyl}) showed significantly enhanced photovoltaic performance than that of PTB7-Th:MA (3.29% versus 0.92%). Moreover, the photovoltaic performance of these polymeric acceptors could be further improved via a terpolymeric strategy. By copolymerizing a small amount of meta-linkages into PA, the optimized terpolymeric acceptors enabled to enhance photovoltaic performance with improved the short-circuit current density (Jsc) and fill factor (FF), resulting in an improved power conversion efficiency (PCE) of 4.03%.

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Acknowledgments

This work was financially supported by the Ministry of Science and Technology of China (No. 2014CB643501), the National Natural Science Foundation of China (Nos. 21634004 and 51403070), and the Foundation of Guangzhou Science and Technology Project (No. 201707020019). Zhi-Cheng Hu thanks the financial support from China Postdoctoral Science Foundation (No. 2017M622684).